1. Field of the Invention
The present invention relates to the circuit for operating light-emitting devices (LED) and a drive scheme to operate such. More specifically, the present invention provides a method to deliver uninterrupted drive current to the LEDs in the array at the event of damage to one or more LED elements in the array.
2. Description of the Prior Art
Light emitting diodes are attracting wide interests in display application in recent years. The applications include direct view screen constructed from organic or inorganic light emitting diodes, backlight for LCD, LED lighting and etc. Its excellent form factor, fast response time, lighter weight, low operating voltage, make it the ideal device for a wide range of applications. Such applications typical comprise a plurality of LEDs in the form of serial or array structure. Whereas the operating life for an individual LED may be acceptable, the collective life time of an LED array containing a large number of LEDs is a serious concern over the reliability of such products. This issue is particularly critical in applications where the replacement of LED unit is not practical.
An LED's light output is readily controlled by the drive current directed thereto. Where a multiple LEDs, each delivering similar light output, is preferred in an application, a string of LED connected in series is typically used, as provided in FIG. 1 where the LED array 100 connected in series, and a current source 103 delivering the drive current. The control of light output is through the adjustment of the current level via a control circuit according to the signals. In such serial construction, a failure of any LED in the string makes the entire string inoperable. The requirement for the reliability of LED thus increases with the number of LEDs.